The present invention relates to a magnetic encoder and a micromotor, and more particularly to a magnetic micro-encoder for detecting the number of rotations and a rotational direction of a motor, and a micromotor including the magnetic micro-encoder.
Conventionally, to detect the number of rotations and a rotational direction of a motor, an encoder has been used which includes a pair of sensors for obtaining both data of an A-phase and a B-phase. This encoder, shown in FIG. 7 for example, includes a rotatable magnetic disk and fixed side magnetic sensors, and it obtains rectangular waves from changes in output voltages of the magnetic sensors according to a rotation of the magnetic disk by putting these output voltages through a comparator. However, in a case of a microminiature encoder, for example, having an external diameter of 5 "PHgr" mm or less, there are problems related to its housing space in an arrangement of electronic components such as magnetic sensors or the like for detecting both an A-phase and a B-phase. Namely, in an arrangement method in which magnetic sensors are arranged in a radial direction of a magnetic disk similarly to the conventional encoder, there is a limitation in reducing a diameter of the magnetic disk, and an arrangement space for the magnetic sensors is required to be in a radial direction of the magnetic disk, so that it is difficult to arrange the magnetic sensors and the magnetic disk in a housing space having a micro-sized diameter. On the other hand, in a case that two magnetic sensors in a rectangular shape are arranged opposite to a surface of a magnetic disk, an arrangement space for magnetic sensors is required to be in an axial direction of the magnetic disk, so that it is advantageous for reducing the diameter of the magnetic disk. In this case, as a method of arrangement for the two magnetic sensors, as shown in FIG. 8, an arrangement method is conceivable such that longitudinal directions of magnetic sensors 26a and 26b are arranged alongside of an inner periphery 23 of a housing. However, when this arrangement is tried inside the inner periphery 23 of a housing space with a micro-sized diameter, these two magnetic sensors 26a and 26b interfere with each other, so that this arrangement method is unacceptable. Further, in a method of arrangement for two magnetic sensors 36a and 36b in a rectangular shape as shown in FIG. 9, a part of housing is cut out so that it is possible to arrange the magnetic sensors 36a and 36b. However, since each of the magnetic sensors 36a and 36b has one pair of input terminals and one pair of output terminals on its diagonal lines, this arrangement complicates a wiring pattern connected to input terminals and output terminals, so that this arrangement method is unacceptable, too.
An object of the present invention is to provide a microminiature magnetic micro-encoder which includes a magnetic disk and two magnetic sensors being arranged in a housing with external diameter of 5 "PHgr" mm or less and a micromotor including this magnetic micro-encoder.
The present inventors conducted dedicated studies of the number of poles of a magnetic disk, a magnetic disk, a positional relationship of magnetic sensors, and an arrangement of magnetic sensors and, as a result, achieved an optimum number of magnetic poles, an optimum positional relationship, and an optimum arrangement for microminiaturizing a magnetic encoder. Thus the present inventors accomplished the present invention.
The magnetic micro-encoder according to the present invention includes: a magnetic disk mounted on an rotation shaft and polarized in an axial direction; a first back yoke mounted on the magnetic disk; two magnetic sensors arranged opposite to a surface of the magnetic disk in an axial direction with a gap therebetween, which are also mounted on a sensor mounting part of a flexible printed substrate in such a manner that longitudinal directions of these magnetic sensors are substantially parallel to a band-formed wiring part of the flexible printed substrate; a second back yoke mounted on a back of the magnetic sensors with the flexible printed substrate intervened therebetween, which is forming a magnetic circuit with the first back yoke and the magnetic disk; and a housing for accommodating the first back yoke, the magnetic disk, the magnetic sensors, and the second back yoke.
The magnetic sensors detect changes of a magnetic flux density and a polarity on a rotating magnetic disk. These magnetic sensors are arranged opposite to a surface of the magnetic disk in an axial direction with a gap therebetween, which are also mounted on a sensor mounting part of a flexible printed substrate in such a manner that longitudinal directions of the magnetic sensors are substantially parallel to a band-formed wiring part of the flexible printed substrate. By adopting this structure, the magnetic sensors can be arranged in a microminiature housing. In addition, a flexible printed substrate is thinner than a generally used glass epoxy substrate, so that it is possible to make a sensor mounting substrate thinner. Accordingly, it is possible to make a length of the micro-encoder shorter.
In the magnetic micro-encoder according to the present invention, the number of magnetic poles of the magnetic disk is defined as 2 (1+4n) (where xe2x80x9cnxe2x80x9d is an integer of 0(zero) or more), and the two magnetic sensors are arranged in such a manner that their positions are open to each other in an angle of 90 degrees from the rotation shaft.
The number of magnetic poles of the magnetic disk is defined as 2 (1+4n) (where xe2x80x9cnxe2x80x9d is an integer of 0(zero) or more), and the magnetic sensors are arranged in such a manner that their positions are open in an angle of 90 degrees from the rotation shaft, in other words, their positions are separated from each other toward a radial direction of the rotation shaft in an angle of 90 degrees with the rotation shaft as the center. In accordance with the above arrangement, a phase difference of output waveforms of the two magnetic sensors, i.e., a phase difference of an A-phase and a B-phase becomes 90 degrees. When the phase difference of output waveforms becomes 90 degrees, allowable cycle variation widths of signal waveforms become maximum, so that detection accuracy in a rotational direction will be improved. In addition, the output waveforms can be easily quadrupled to improve a resolution.
In the magnetic micro-encoder according to the present invention, the number of magnetic poles of the magnetic disk is defined as 2 (3+4n) (where xe2x80x9cnxe2x80x9d is an integer of 0(zero) or more), and the two magnetic sensors are arranged in such a manner that their positions are open to each other in an angle of 90 degrees from the rotation shaft.
The number of magnetic poles of a magnetic disk is defined as 2 (3+4n) (where xe2x80x9cnxe2x80x9d is an integer of 0(zero) or more), and magnetic sensors are arranged in such a manner that their positions are open in an angle of 90 degrees from the rotation shaft, in other words, their positions are separated from each other toward a radial direction of the rotation shaft in an angle of 90 degrees with the rotation shaft as the center. In accordance with the above arrangement, a phase difference of output waveforms of the two magnetic sensors, i.e., a phase difference of an A-phase and a B-phase becomes 90 degrees. When the phase difference of output waveforms becomes 90 degrees, allowable cycle variation widths of signal waveforms become maximum, so that detection accuracy in a rotational direction will be improved. In addition, the output waveforms can be easily quadrupled to improve a resolution.
The magnetic micro-encoder according to the present invention has a structure in which a cut-out portion is formed on the housing for drawing out the band-formed wiring part therethrough, the sensor mounting part is formed along a shape of the cut-out portion, and the flexible printed substrate is engaged with the housing to be fixed therein.
The flexible printed substrate is fixed in the housing in such a manner that a side surface of the sensor mounting part abuts on an inner periphery surface of the housing and on the cut-out portion of the housing. As described above, the magnetic micro-encoder of the present invention has a structure in which the flexible printed substrate is engaged with the housing to be fixed therein. The sensor mounting part of the flexible printed substrate is formed along the cut-out portion of the housing and the inner periphery surface of the housing, so as to prevent a positional displacement of the flexible printed substrate in a rotational direction of the rotation shaft. Therefore, a fixing strength of the flexible printed substrate can be improved.
The magnetic micro-encoder according to the present invention has a fixing structure in which a stepped portion is formed on an inner surface of the housing, the second back yoke is engaged with the housing with the flexible printed substrate intervened therebetween, and the flexible printed substrate is sandwiched between the stepped portion and the second back yoke to be fixedly arranged therebetween in a mechanical manner.
The second back yoke is formed along the cut-out portion of the housing and along the inner periphery surface of the housing and is press fitted into or inserted and adhered into the housing, in such a manner that a side surface of the second back yoke abuts on the inner periphery surface and the cut-out portion of the housing. By sandwiching the flexible printed substrate between the stepped portion formed on the inner surface of the housing and the second back yoke, the fixing strength of the flexible printed substrate in an axial direction of the housing can be improved.
In the magnetic micro-encoder according to the present invention, the second back yoke doubles as an end cap to cover an opening of the housing.
The opening of the housing is on the opposite side of the magnetic sensors. Since the second back yoke doubles as the end cap, the number of components can be reduced, and a length of the magnetic micro-encoder can be shortened. Namely, the second back yoke combines the role of the magnetic circuit formation, the flexible substrate fixation, and the end cap.
In the magnetic micro-encoder according to the present invention, the housing is formed in a substantially cylindrical shape, and this housing is formed in an external diameter of 5 "PHgr" mm or less.
In the magnetic micro-encoder, the housing is formed in an external diameter of 5 "PHgr" mm or less, more preferably, the housing is formed in an external diameter ranging from 2 "PHgr" mm to 4 "PHgr" mm. In addition, the magnetic micro-encoder of the present invention has a structure in which an external diameter of the encoder can be reduced according to the miniaturization of the magnetic sensors.
The micromotor according to the present invention has the magnetic micro-encoder provided therein.
The micromotor according to the present invention has a speed reducer provided therein.
The speed reducer is placed on an output shaft of the micromotor and reduces the speed by predetermined speed reduction ratio. The speed reducer is constructed with, for example, a plurality of planetary gears. The placement of this speed reducer increases the number of output waveforms (pulses) of the encoder according to a movement of the motor output shaft (output shaft of the speed reducer) and improves the resolution, so that the micromotor can be controlled more precisely.